The Repair of Single-Strand Breaks in a Radiosensitive Mutant of Micrococcus radiodurans

The kinetics of x-ray-induced single-strand break rejoining have been studied in wild-type M. radiodurans and a radiosensitive mutant, UV17. The initial fast rejoining reaction observed in wild-type cells in growth medium was absent in UV17. Studies in which irradiated cells were allowed to repair u...

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Bibliographic Details
Published in:Radiation research 1974-02, Vol.57 (2), p.260-275
Main Authors: Bonura, T., Bruce, A. K.
Format: Article
Language:English
Subjects:
BIOLOGICAL RADIATION EFFECTS
CATALYSIS
Cell growth
DNA
DNA Damage
DNA Repair
DNA Replication - radiation effects
DNA, Bacterial - radiation effects
DNA- STRAND BREAKS
ENZYMES
Escherichia coli
Hydrolysis
Irradiation
Kinetics
METABOLISM
Methylnitronitrosoguanidine
Micrococcus
Micrococcus - genetics
Micrococcus - radiation effects
MICROCOCCUS RADIODURANS- MUTANTS
Molecular weight
Mutagenesis
MUTANTS- RADIOSENSITIVITY
N48310 -Life Sciences-Radiation Effects on Microorganisms- -Basic Studies
Phosphates
PHOTON BEAMS
Radiation tolerance
RADIOINDUCTION
STRAND BREAKS- BIOLOGICAL REPAIR
Ultraviolet Rays
X RADIATION RADIOINDUCTION
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Summary:The kinetics of x-ray-induced single-strand break rejoining have been studied in wild-type M. radiodurans and a radiosensitive mutant, UV17. The initial fast rejoining reaction observed in wild-type cells in growth medium was absent in UV17. Studies in which irradiated cells were allowed to repair under various conditions confirm that a buffer-mediated rejoining system is absent in UV17 while rejoining of strand breaks under growth conditions is slower but not absent. DNA breakdown is more extensive in UV17 although its rate is similar to that of the wild-type. In both strains the x-ray-induced DNA synthesis delay and the time for maximal release of acid-soluble material corrlelate. In vitro studies show the capacity of lysates of wild-type and mutant cells to catalyze the incorporation of deoxyribonucleotide triphosphates into acid-insoluble material are similar while DNase activity in the mutant is much greater than in the wild type. The in vitro data are correlated with the in vivo observations and indicate that the sensitivity of UV17 to ionizing radiation may be the result of an inhibition of DNA polymerase-mediated repair and not a consequence of an exr or lex type of mutation as has been previously thought.
ISSN:0033-7587
1938-5404
DOI:10.2307/3573832